The present invention pertains to the field of computer systems. More particularly, the present invention relates to storage controllers for controlling data transfers between one or more host processing systems and one or more data storage subsystems.
Computer systems sometimes handle valuable or irreplaceable data. Data maintained by a computer system may be of vital importance, for example, in business applications such as airline reservations, bank account management, electronic funds transfers, shipping and receiving, and inventory control. Consequently, there is a need to ensure that valuable data is adequately protected against loss or damage.
It is common to store large volumes of data on non-volatile mass storage devices, such as magnetic or optical disks. Occasionally, however, a mass storage device will fail, resulting in the loss of stored data. Consequently, it is a common practice to store a back-up copy of data that is considered valuable on a separate, back-up storage device. For practical reasons, however, it is often necessary to locate the back-up storage device in the same geographic vicinity as the primary storage device. As a result, both the primary data and the back-up copy may be lost or destroyed due to fire, theft, vandalism, or natural disaster. Hence, there is a need for the capability to store multiple back-up copies of data in geographically separate locations, while still permitting quick and easy access by a host computer to any back-up copy.
One aspect of the present invention is a storage controller configured to selectively operate in either an active mode or a quiescent mode. When in the active mode, the storage controller provides a host processing system with access to a storage array. When in the quiescent mode, the storage controller monitors the status of an active storage controller that provides the host processing system with access to the storage array and responds to a failure of the active storage controller by automatically switching to the active mode.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.